The present invention relates to a process for the production of polybutadiene having a high cis-1,4-content.
A process is disclosed in Canadian Pat. No. 934742 for the polymerization of conjugated diolefins in the presence of catalysts which are compounds of metals of Group VIII and organometallic compounds of metals of Group III of the Periodic Table of the Elements to obtain polymers having essentially a cis-1,4-content. In this process, homogeneous solutions of catalysts consisting of a cobalt compound and an alkyl aluminum halide are employed. The polymerizing medium is constituted by cycloaliphatic and preferably aromatic hydrocarbons, such as, for example, benzene or mixtures made from these solvents and aliphatic hydrocarbons.
Another process for the production of polybutadiene having a high cis1,4-content is known from U.S. Pat. No. 3,066,127. In this process, 1,3-butadiene is polymerized in a non-aqueous solution with one of several compounds of cobalt and/or nickel and one or several organoaluminum compounds, preferably alkyl aluminum compounds, as the catalyst in the presence of a specified quantity of water. The solvent is preferably constituted by aromatic hydrocarbons. The utilization of benzene as the sole diluent is a preferred embodiment of the polymerization of butadiene with the catalyst claimed. On the other hand, aliphatic hydrocarbons can only be used in combination with cyclic or aromatic hydrocarbons.
As can be seen from these comments on the relevant state of the art processes, aromatic hydrocarbons, preferably benzene, are favored as the solvent in the production of, for example, polybutadienes having a high cis-1,4-content using soluble cobalt- and/or nickel-containing catalysts of the Ziegler-Natta type. The reason is that these aromatic hydrocarbons support the formation of soluble catalysts as well as being especially good solvents for the polymer formed.
Despite these good properties, however, aromatic hydrocarbons, because of their toxicity, and especially benzene, because of its carcinogenic effect, pose a great danger to the environment. Consequently, there has been an ongoing effort to replace the toxic aromatic solvents with less toxic ones.
Thus, a process is described in U.S. Pat. No. 4,020,255 for the production of polybutadiene having a high cis-1,4-content in which the butadiene is polymerized in a mixture using an aliphatic or cycloaliphatic solvent. The polymerization catalyst therein consists of (a) a trialkyl aluminum compound, (b) a nickel-carboxylic acid salt and (c) a boron trifluoride etherate. However, such catalysts are very expensive and difficult to handle. A process is also described in Canadian Pat. No. 795,860 (Chem. Abstr. 62, 6658d) wherein a catalyst of (a) diethylaluminum chloride, (b) water and (c) cobalt dioctoate is used to polymerize butadiene. Although general aromatic and aliphatic solvents are disclosed, the specific solvent utilized is benzene and the catalyst components are employed in the sequence (b), (a) and then (c).